Patent Document 1 is an example that discloses a method to determine a distance using a reception time lag between an infrared ray signal and an ultrasonic wave signal. Patent Document 2 discloses an electronic pen system as an example of a conventional position detection method using an ultrasonic wave. The position detection system includes an electronic pen having a function to transmit an ultrasonic wave signal having a specified waveform in a constant period and an infrared ray trigger signal in a fixed period and a reception portion to receive transmitted two signals, and the reception portion determines the position of the electronic pen by the arrival time of the trigger signal and the arrival time of the ultrasonic wave.
Patent Document 3 discloses a method to eliminate reverberation for an ultrasonic wave transmission/reception system by assigning a band width of impedance of an ultrasonic sensor, transmission band width of a transmission means, reception band width of a reception means and pass-band width of a transmission/reception switching circuit in a predetermined relation.